standard atmosphere

Examples of standard atmosphere in the following topics:

• Gauge Pressure and Atmospheric Pressure

  • In most measurements and calculations, the atmospheric pressure is considered to be constant at 1 atm or 101,325 Pa, which is the atmospheric pressure under standard conditions at sea level.
  • Atmospheric pressure is due to the force of the molecules in the atmosphere and is a case of hydrostatic pressure.
  • Depending on the altitude relative to sea level, the actual atmospheric pressure will be less at higher altitudes and more at lower altitudes as the weight of air molecules in the immediate atmosphere changes, thus changing the effective atmospheric pressure.
  • Atmospheric pressure is a measure of absolute pressure and can be affected by the temperature and air composition of the atmosphere but can generally be accurately approximated to be around standard atmospheric pressure of 101,325 Pa.
  • In this equation p0 is the pressure at sea level (101,325 Pa), g is the acceleration due to gravity, M is the mass of a single molecule of air, R is the universal gas constant, T0 is the standard temperature at sea level, and h is the height relative to sea level.

• Properties of Oxygen

  • Oxygen is a highly reactive nonmetallic element; it is a strong oxidizing agent with high electronegativity and forms O2 at Standard Temperature and Pressure (STP).
  • Oxygen is an important part of the atmosphere and is necessary to sustain terrestrial life.
  • At standard temperature and pressure (STP), two atoms of the element bind to form dioxygen, a colorless, odorless, tasteless diatomic gas with the formula O2.
  • Elemental O2 only began to accumulate in the atmosphere after the evolutionary appearance of photosynthetic organisms, roughly 2.5 billion years ago.
  • At 25 °C and 1 standard atmosphere (101.3 kPa) of air, freshwater contains about 6.04 milliliters (mL) of oxygen per liter, whereas seawater contains about 4.95 mL per liter.

• Standard Entropy

  • The standard entropy of a substance (its entropy at 1 atmospheric pressure) helps determine if a reaction will take place spontaneously.
  • The standard entropy of a substance is its entropy at 1 atm pressure.
  • Some typical standard entropy values for gaseous substances include:
  • Scientists conventionally set the energies of formation of elements in their standard states to zero.
  • The standard entropy of reaction helps determine whether the reaction will take place spontaneously.

• Standard Free Energy Changes

  • The standard Gibbs Free Energy is calculated using the free energy of formation of each component of a reaction at standard pressure.
  • These same definitions apply to standard enthalpies and internal energies.
  • Don't confuse these thermodynamic standard states with the "standard temperature and pressure" (STP) widely employed in gas law calculations.
  • To accomplish this, combine the standard enthalpy and the standard entropy of a substance to get the standard free energy of a reaction:
  • As with standard heats of formation, the standard free energy of a substance represents the free energy change associated with the formation of the substance from the elements in their most stable forms as they exist under the standard conditions of 1 atm pressure and 298K.

• Standard Reduction Potentials

  • Standard reduction potentials provide a systematic measurement for different molecules' tendency to be reduced.
  • The standard reduction potential is defined relative to a standard hydrogen electrode (SHE) reference electrode, which is arbitrarily given a potential of 0.00 volts.
  • The values below in parentheses are standard reduction potentials for half-reactions measured at 25 °C, 1 atmosphere, and with a pH of 7 in aqueous solution.
  • Historically, many countries, including the United States and Canada, used standard oxidation potentials rather than reduction potentials in their calculations.
  • These are simply the negative of standard reduction potentials, so it is not a difficult conversion in practice.

• Properties of Nitrogen

  • Nitrogen in its elemental form is a non-metallic gas that makes up 78 percent of Earth's atmosphere.
  • Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.09 percent of Earth's atmosphere by volume.
  • However, as on Earth, nitrogen and its compounds occur commonly as gases in the atmospheres of planets and moons.
  • Nitrogen absorption leads to significant absorption of ultraviolet radiation in the Earth's upper atmosphere and the atmospheres of other planetary bodies.
  • As a modified atmosphere, pure or mixed with carbon dioxide, to preserve the freshness of packaged or bulk foods

• Atmospheric Perspective

• Evidence of Global Climate Change

  • Global climate change can be understood by analyzing past historical climate data, such as atmospheric CO2 concentrations in ice cores.
  • Carbon dioxide levels in the atmosphere have historically cycled between 180 and 300 parts per million (ppm) by volume.
  • Advances in agriculture increased the food supply, which improved the standard of living for people in Europe and the United States.
  • By measuring the amount of CO2 trapped in ice, scientists can determine past atmospheric CO2 concentrations.
  • The atmospheric concentration of CO2 has risen steadily since the beginning of industrialization.

• Atmospheric Perspective

  • Atmospheric perspective refers to the effect the atmosphere has on the appearance of an object as it is viewed from a distance.
  • Atmospheric perspective, also known as aerial perspective, refers to the effect the atmosphere has on the appearance of an object as it is viewed from a distance.
  • In addition to creating a sense of depth, atmospheric perspective can be used to express environmental conditions and time of day in a work of art.
  • Atmospheric perspective was used in Pompeian Second Style paintings, dating as early as 30 BCE.
  • One of the earliest usages of atmospheric perspective is evident in this mural from Pompeii.

• Ozone

  • Ozone is formed from dioxygen by the action of ultraviolet light and also atmospheric electrical discharges.
  • It is present in low concentrations throughout the Earth's atmosphere.
  • In total, ozone makes up only 0.6 parts per million of the atmosphere.
  • In standard conditions, ozone is a pale blue gas that condenses at progressively cryogenic temperatures to a dark blue liquid and finally a violet-black solid.
  • It is also unstable at high concentrations, decaying to ordinary diatomic oxygen (with a half-life of about half an hour in atmospheric conditions):